diff --git a/airbyte_cdk/sources/declarative/concurrent_declarative_source.py b/airbyte_cdk/sources/declarative/concurrent_declarative_source.py
index 8d5ac3ab2..ba76b0a39 100644
--- a/airbyte_cdk/sources/declarative/concurrent_declarative_source.py
+++ b/airbyte_cdk/sources/declarative/concurrent_declarative_source.py
@@ -211,7 +211,8 @@ def _group_streams(
             # so we need to treat them as synchronous
 
             supports_file_transfer = (
-                "file_uploader" in name_to_stream_mapping[declarative_stream.name]
+                isinstance(declarative_stream, DeclarativeStream)
+                and "file_uploader" in name_to_stream_mapping[declarative_stream.name]
             )
 
             if (